1. Field of Invention
The present invention relates to an ink composition for ink jet recording that can produce print mottle-free and high-quality recorded matters on various recording media, especially even on recording media having a low level of water absorption such as synthetic papers and printing papers for running-on.
2. Background Art
Ink jet recording is a printing method wherein droplets of an ink are ejected and deposited on recording media, such as paper, to perform printing. An innovative advance of a recent ink jet recording technique has made it possible to realize the production of images having quality comparable to images produced by silver salt photography or images yielded by high-definition printing realized only by offset printing. This trend has led to the development of inks for ink jet recording that can realize images having a high level of glossy impression comparable to the gloss of images produced by silver salt photography, using the so-called specialty papers that are recording media having a high level of gloss comparable to photographic paper, art paper and the like used in the field of silver salt photography and offset printing. Further, inks for ink jet recording that can realize image quality comparable to the image quality of images produced by silver salt photography even on plain paper have also been developed.
The widespread use of techniques for forming images from digital data in recent years has led to an increased need for digital color proofs (DTPs) particularly in the field of printing, and an ink jet recording method has also become applied to DTPs. The color reproduction and stability reproduction of printed matters are required of DTPs. Accordingly, when proofs are prepared by the ink jet recording method, specialty paper for ink jet recording has been generally used.
In applications for color proof, however, ink jet recording on printing paper for running-on rather than specialty papers has been desired. Further, when prints produced by ink jet recording directly on printing paper for running-on without use of specialty papers can be used as a final proof sample, it is considered that proof cost can be significantly reduced. Furthermore, synthetic papers, which are widely used in the field of printing and are produced by mixing a polyethylene resin or a polyester resin, for example, with an inorganic filler and forming the mixture into a film, have recently drawn attention as materials that have excellent recyclability and are environmentally friendly.
The printing paper for running-on is a coated paper having on its surface a coating layer for receiving an oil-based ink. In the printing paper for running-on, however, the capability of the coating layer to absorb ink is disadvantageously poor. Therefore, when water-based pigment inks, which have been generally used in ink jet recording, are used, the penetrability of the inks into recording media (printing paper for running-on) is so low that feathering or bleeding or uneven coagulation sometimes occurs in images.
In order to solve the problems, for example, Japanese Patent Application Laid-Open No. 194500/2005 (patent document 1) discloses a pigment-based ink that can yield images having reduced feathering or bleeding and, at the same time, having excellent gloss on specialty papers by using a polysiloxane compound as a surfactant and adding an alkanediol such as 1,2-hexanediol as a solubilizer. Further, Japanese Patent Application Laid-Open No. 213179/2003 (patent document 2) proposes that a high-quality image is produced by adding a water soluble organic solvent such as glycerin or 1,3-butanediol to ink to regulate the penetration of the ink into recording media.